1. Field of the Invention
The present invention relates to improved hardenable resin compositions for consolidating particulate solids coated therewith and to methods of consolidating particulate solids in subterranean zones using the resin compositions.
2. Description of the Prior Art
Various resin compositions and methods have been developed for consolidating particulate solids such as sand into hard permeable packs in subterranean zones. The compositions and methods are useful in preventing loose or incompetent sand in subterranean formations from being produced from the formations along with formation fluids such as hydrocarbons and/or water. The consolidated particulate solid packs reduce or prevent the migration and production of sand with produced fluids when the packs are located between the producing formation and the well bore penetrating the formation.
A technique which has heretofore been utilized for consolidating loose or incompetent sand in a subterranean zone penetrated by a well bore comprises pumping a hardenable resin composition in a carrier fluid into the zone by way of the well bore whereby the loose or incompetent sands are coated with the resin composition and then causing the resin composition to harden whereby the loose or incompetent sands are consolidated into a hard permeable pack.
Another technique which has heretofore been utilized for forming a hard permeable particulate solid pack in a subterranean zone penetrated by a well bore comprises suspending the particulate solids in a viscous carrier fluid and coating the solids with a hardenable resin composition on the surface and then pumping the suspension by way of the well bore into the subterranean zone whereby the resin coated particulate solids are deposited therein. The hardenable resin composition on the deposited particulate solids is caused or permitted to harden whereby a consolidated permeable particulate solid pack is formed between the well bore and loose or incompetent sand in the formation.
Hydrocarbon producing wells are often stimulated by hydraulic fracturing treatments. In such hydraulic fracturing treatments, a viscous fracturing fluid which also functions as a carrier fluid is pumped into a producing zone to be fractured at a rate and pressure such that one or more fractures are formed in the zone. Particulate solids for propping the fractures, commonly referred to in the art as "proppant," are suspended in a portion of the fracturing fluid so that the particulate solids are deposited in the fractures when the fracturing fluid is broken, usually by a breaker composition included in the fracturing fluid, whereby the fracturing fluid reverts to a thin fluid and returns to the surface. The proppant functions to prevent the fractures from closing so that conductive channels are formed through which produced fluids can readily flow.
In order to prevent the subsequent flow-back of proppant as well as loose or incompetent sand in the fractured zone with fluids produced therefrom, at least a portion of the proppant has heretofore been coated with a hardenable resin composition which is caused to harden and consolidate the proppant in the zone. Typically, the resin composition coated proppant is deposited in the fracture after a larger quantity of uncoated proppant has been deposited therein. That is, the last portion of the proppant deposited in each fracture, referred to in the art as the "tail-end" portion, is coated with the hardenable resin composition. When the viscous fracturing fluid which is the carrier fluid for the proppant is broken and reverts to a thin fluid as described above, the resin coated proppant is deposited in the fractures and the fractures close on the proppant. The partially closed fractures apply pressure on the resin coated proppant whereby the proppant particles are forced into contact with each other while the resin composition hardens. The hardening of the resin composition under pressure brings about the consolidation of the resin coated proppant particles into a hard permeable pack having sufficient compressive strength to prevent unconsolidated proppant and formation sand from flowing out of the fractures with produced fluids.
In fracture treatments carried out in an unconsolidated formation, good consolidation of proppant is required in the perforations which extend from inside the well bore through casing and cement into the unconsolidated formation as well as in the fractured portions of the unconsolidated formation surrounding the well bore. That is, the tail-end portion of the proppant which is deposited in the perforations and in the fractures, is coated with a hardenable resin composition and caused to harden. The resulting consolidated proppant in the perforations and fractures contributes to the prevention of proppant flow-back. However, there is often little closure pressure applied to the resin coated proppant in the fractures in an unconsolidated formation and there is no closure pressure applied to the resin coated proppant in the perforations. As a result, the consolidated permeable packs formed in the perforations and fractures often have less than sufficient compressive strength to prevent unconsolidated proppant and formation sand from flowing out of the perforations and fractures.
The above problem is complicated when the viscous carrier fluid (the fracturing fluid) is a cross-linked gelled fluid containing a breaker which does not break for a relatively long period of time during which the resin composition coated on the proppant hardens. At high temperatures and particularly temperatures above about 200.degree. F., resin compositions harden quickly and if the viscous carrier fluid has not broken, the resin coated particulate proppant particles are separated from each other by films of the viscous carrier fluid. As a result of the presence of the carrier fluid films, the proppant does not sufficiently consolidate and proppant flow-back occurs. Thus, when resin coated particulate solids are consolidated in subterranean zones where there is little or no closure pressure exerted on the resin coated particulate solids or when a carrier fluid used to carry resin coated particulate solids into a subterranean zone does not break before the resin hardens, or both, sufficient consolidation of the particulate solids often does not take place and proppant flow-back occurs.
Thus, there are needs for improved hardenable resin compositions and methods for consolidating particulate solids coated with the resin compositions in subterranean zones which produce good consolidations with or without closure pressure exerted thereon or when the particulate solids are separated by films of an unbroken viscous carrier fluid in the zone, or both.